There are various formulations to ensure fire-resistance in hydraulic fluids, but water glycols remain the most commonly used, decades after their introduction.
The pace of technological change, along with manufacturing cost structures, combine to place a wide number of skills and technologies beyond the practical experience of machine shops and similar operations. Hydraulics, widely used to power production machinery, is one of those areas of specialization that challenges operators’ expertise. Here is a helpful guide to understanding hydraulic fluids and their performance capabilities.
Although new technologies are continually improving the performance and safety of hydraulic fluids, the most common base for hydraulic fluids remains petroleum oil because of its low cost and high performance. Many hydraulic components are designed with petroleum oil in mind, and often the performance criteria of other fluids are measured against that of petroleum oil, as oil is generally regarded as the standard for hydraulic fluid performance.
In many applications petroleum oil-based fluids cannot be used because of their high flammability. For any hydraulic system that operates close to open flames and hot surfaces that can provide a source of ignition, a fire-resistant fluid is the best choice.
When compared to petroleum oil, fire-resistant fluids need to be selected based on required system performance, cost and stability. Selecting the right fire-resistant fluid often means striking a compromise between system needs and fluid performance characteristics to arrive at a solution that both minimizes cost and maximizes the desired health and safety benefits.
There are four major groups of fire-resistant hydraulic fluids (FRHFs): HFA or high-water containing fluids; HFB or invert emulsions; HFC which are water glycols; and HFD or water-free fluids, including synthetic esters, natural esters and polyalkylene glycols (PAGs).
HFA fluids are also called high-water-content fluids (HWCF) or 95/5 fluids, because they were originally to be a 5% emulsion of oil in water. Oil adds lubrication and corrosion protection, but the bulk of the fluid is water, so the strengths and weaknesses of water are still largely present with HFA fluids.
For example, HFA fluids are extremely fire-resistant, but they require equipment that has been specifically designed to run with water. Therefore, HFA fluids cannot be substituted for petroleum oil in typical hydraulic equipment.
HFA fluids are used widely in steel mills and coal mines, where the equipment is designed with HFA fluids in mind. Traditional oil-based HFA fluids are still in use, but they are being replaced with synthetic products that offer better lubrication, consistency, corrosion protection and resistance to microbiological growth.